Unlike Esa Helttula's other apps, which allow kids to practice specific skills through a no-nonsense kind of interface, Esa's latest app, for the iPad, gives kids a playground of sorts to play around ...

Most people will probably remember the times tables from primary school quizzes. There might be patterns in some of them (the simple doubling of the 2 times table) but others you just learnt by rote.

Start by completing the calculation using positive numbers first, then use the sign rules to find the sign of the answer. Image caption, This multiplication table includes both positive and negative ...